Projection display device

ABSTRACT

Provided is a projection display device for displaying a time period of one frame of stereo image as a first modulation period. The projection display device includes: a light source for emitting illumination light; a spatial light modulator for modulating the illumination light according to a plurality of frames of two-dimensional images corresponding to a stereo image to be displayed, and sequentially emitting, within the first modulation period, image light corresponding to the plurality of frames of the two-dimensional images; an angle deflection apparatus arranged in an emergent optical path of the image light and used for deflecting the image light corresponding to the plurality of frames of two-dimensional images to different angles for emission; and a projection screen for displaying the image light deflected by the angle deflection apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation-in-part of Internationalapplication PCT/CN2020/103562, filed on Jul. 22, 2020, which claimspriority to Chinese Patent Application No. 201910691347.8, filed on Jul.29, 2019, the content of which is incorporated herein by reference inits entirety.

TECHNICAL FIELD

The present disclosure relates to the field of projection technologies,and in particular, to a projection display device.

BACKGROUND

This part is intended to provide background or context for specificimplementations of the present disclosure in the claims. The descriptionherein is not recognized as the prior art by virtue of inclusion in thispart.

Generally, three-dimensional (3D) projection display depends on a highrefresh rate of a projector, such that images at different angles can beprojected in display time of one frame of stereo image. However, asufficient refresh rate is required to display an image at each angle.

SUMMARY

The present disclosure provides a projection display device capable ofeffectively improving an image refresh rate (frame rate), to project atwo-dimensional (2D) image from a plurality of angles to obtain a stereoimage.

The present disclosure provides a projection display device, where aperiod in which one frame of stereo image is displayed is referred to asa first modulation cycle, and the projection display device includes:

a light source, configured to emit illumination light;

a spatial light modulator, configured to modulate the illumination lightbased on a plurality of frames of 2D images corresponding to ato-be-displayed stereo image, and sequentially emit, in the firstmodulation cycle, image light corresponding to the plurality of framesof 2D images;

an angle deflection apparatus, disposed on an emergent optical path ofthe image light, and configured to deflect the image light correspondingto the plurality of frames of 2D images to different angles foremission; and

a projection screen, configured to display the image light deflected bythe angle deflection apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

To describe the technical solutions in the embodiments/implementationsof the present disclosure more clearly, the following briefly describesthe accompanying drawings required for describing theembodiments/implementations. Apparently, the accompanying drawings inthe following description show merely some embodiments/implementationsof the present disclosure, and a person of ordinary skill in the art mayfurther derive other drawings from these accompanying drawings withoutcreative efforts.

FIG. 1 is a schematic structural diagram of a projection display deviceaccording to the present disclosure;

FIG. 2 is a principle diagram related to a second modulation cycle;

FIG. 3 is a principle diagram of a correspondence between illuminationbrightness and an LSB in a second modulation cycle according to anembodiment of the present disclosure;

FIG. 4 is a principle diagram of a correspondence between illuminationbrightness and an LSB in a second modulation cycle according to anotherembodiment of the present disclosure;

FIG. 5 is a schematic structural diagram of an angle deflectionapparatus shown in FIG. 1 in an implementation; and

FIG. 6 is a schematic structural diagram of an angle deflectionapparatus shown in FIG. 1 in another implementation.

List of reference numerals Projection display device 100 Light source110 Spatial light modulator 150 Angle deflection apparatus 170 Controlapparatus 190 Image light I, I1, I2, I3 Guide array W Guide portion W1,W2, W3

The present disclosure is further described in the following detaileddescription with reference to the accompanying drawings.

DETAILED DESCRIPTION

According to a pulse width modulation (PWM) method used for atraditional digital micro-mirror device (DMD), a frame rate formonochrome display with a bit depth of 8 is limited to about 180 Hz. Ifeach frame of image is synthesized by three frames of images ofdifferent base colors, a frame rate of each frame of image is 60 Hz, inother words, 60 images of three base colors are refreshed every second,which is far from enough for multi-angle 3D projection display.

To make the objectives, features, and advantages of the presentdisclosure more comprehensible, the present disclosure is described indetail below with reference to the accompanying drawings and specificembodiments. It should be noted that without conflict, the embodimentsof the present disclosure and features of the embodiments may becombined with each other.

Many specific details are set forth in the following description tofacilitate a full understanding of the present disclosure. The describedembodiments are merely some but not all of the embodiments of thepresent disclosure. All other embodiments obtained by a person ofordinary skill in the art based on the embodiments of the presentdisclosure without creative efforts shall fall within the protectionscope of the present disclosure.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by those skilled in thetechnical field of the present disclosure. The terms used in thespecification of the present disclosure herein are only for the purposeof describing specific embodiments, and are not intended to limit thepresent disclosure.

As shown in FIG. 1, the present disclosure provides a projection displaydevice 100, which may be a projection display device for displaying astereo image, such as a cinema projector, an engineering projector, amicro projector, or a laser television. The projection display device100 includes a light source 110, a spatial light modulator 150, an angledeflection apparatus 170, a control apparatus 190, a projection lens(not shown in the figure), and a projection screen (not shown in thefigure). The light source 110 is configured to emit illumination light.The spatial light modulator 150 is configured to modulate theillumination light based on a plurality of frames of 2D imagescorresponding to one frame of stereo image to obtain image light. Theangle deflection apparatus 170 is configured to deflect image lightcorresponding to different frames of 2D images to different deflectionangles. Image light emitted by the angle deflection apparatus 170 andtransmitted at different deflection angles is projected onto theprojection screen after passing through the projection lens. Theprojection screen is configured to receive image light with differentdeflection angles to display a stereo image.

In order to more clearly describe a projection display principle of thepresent disclosure, a period in which the projection display device 100displays one frame of stereo image is referred to as a first modulationcycle, which is determined by a refresh rate of a 3D video. Under a samerefresh rate, in order to present the 3D video, a plurality of frames of2D images need to be modulated in time of modulating one frame of 2Dimage in a 2D video. The present disclosure divides the first modulationcycle determined based on the refresh rate into a plurality of secondmodulation cycles. The projection display device 100 reduces modulationtime of a single frame of 2D image to emit image light corresponding toa 2D image in a shorter cycle (second modulation cycle), and then emitsthe image light of the plurality of frames of 2D images at differentdeflection angles in the first modulation cycle. The plurality of framesof 2D images transmitted in different directions are synthesized intoone frame of stereo image to realize 3D display.

In one embodiment, the control apparatus 190 is configured to receive avideo signal. The video signal is a stereo image signal. Each frame ofstereo image signal includes a plurality of frames of 2D original imagesignals, and each frame of 2D original image signal corresponds to a 2Dimage with a projection angle. However, the projection anglescorresponding to the 2D original image signals received by the controlapparatus 190 may be inconsistent with a plurality of fixed projectionangles provided by the projection display device 100. Therefore, afterreceiving the video signal, the control apparatus 190 first obtainscorresponding stereo image data based on 2D original image data of theplurality of angles, splits the stereo image data to obtain a 2D imagecorresponding to a spatial angle that can be obtained by the angledeflection apparatus of the projection display device 100 throughdeflection, and transmits the obtained 2D image to the spatial lightmodulator 150.

The light source 110 may be a pure laser light source for emitting laserlight as the illumination light. The light source 110 may include lasersof three base colors, such as red, green, and blue lasers, to emit theillumination light including the three base colors. In animplementation, the light source 110 is a hybrid laser and fluorescentlight source, which includes an excitation light source and a wavelengthconversion apparatus. The excitation light source includes an illuminantfor emitting laser light as excitation light, and the excitation lightis used to excite a wavelength conversion material on a surface of thewavelength conversion apparatus, so as to generate excited light with adifferent color from the excitation light. The excited light and somenon-converted excitation light are emitted from the light source as theillumination light. In an implementation, the light source 110 emitsillumination light of a variety of base colors by timing, for example,emits red illumination light, green illumination light, and blueillumination light by timing. In an embodiment, the light source mayalternatively be an LED light source.

In a first implementation of the present disclosure, the controlapparatus 190 is configured to send a light source control signal, andthe light source 110 is configured to emit the illumination light basedon the light source control signal. The first modulation cycle includesa plurality of second modulation cycles, and the spatial light modulator150 is configured to emit, in each second modulation cycle, image lightcorresponding to one frame of 2D image. Compared with a traditionalprojection display device for projecting a 2D image, a projectiondisplay device for displaying a stereo image needs to obtain more imageframes through modulation in preset display time of one frame of image,in other words, the projection display device needs to have a higherimage refresh rate. The control apparatus 190 controls, in each secondmodulation cycle, non-constant illumination light emitted by the lightsource 110, and controls a time length corresponding to an LSB of thespatial light modulator 150 in the second modulation cycle, to achieveshorter modulation time under joint action of the brightness-varyinglight source and a modulation mechanism of the spatial light modulator,while ensuring image quality of a modulated 2D image (meeting a bitdepth requirement). In other words, the spatial light modulator canobtain, through modulation in the second modulation cycle, a brightnessset or grayscale set meeting the bit depth requirement.

We know that a computer uses a counting unit referred to as a “bit” torecord data representing a color, so as to display the color. For animage with a display bit depth of 8, a minimum grayscale value is 0, anda maximum grayscale value is 2⁸−1=255. There are 254 grayscale statesbetween the minimum grayscale value and the maximum grayscale value, andeach grayscale state corresponds to a different grayscale value.

A bit depth is a quantity of bits required by the computer to representgrayscale information of a pixel in a grayscale image. When the bitdepth is larger, namely, more bits are required, there is a smallerdifference between adjacent grayscale values, numerical sampling ofsimulation information is less obvious, grayscale difference transitionin the image is more natural and smoother, and an image contrast isgreater. Therefore, the image with the display bit depth of 8 can have2⁸=256 grayscale values.

Assuming that a bit depth of a 2D image emitted by a projection deviceis 8 as required, the spatial light modulator is required to be able toemit 2⁸=256 grayscale states (illumination brightness) in the secondmodulation cycle.

The light source control signal can be used to change the lightbrightness of the corresponding illuminant in the light source 110 byadjusting a driving current or driving voltage of the light source 110.Generally, brightness of the illumination light increases with anincrease of the driving current/driving voltage of the light source 110.However, the illuminant is more likely to be damaged if it iscontinuously driven for a long time at a driving current/driving voltageexceeding a rated current/rated voltage.

Generally, when the light source is continuously driven at its ratedcurrent, the light brightness is rated brightness of the light source.In an existing projection device, the spatial light modulator adopts aPWM modulation method, and the light source works in a continuousdriving mode, in other words, the light source emits illumination lightwith constant brightness to the spatial light modulator. The drivingcurrent of the light source is its rated current, and the brightness ofthe illumination light is the rated brightness of the light source. Inthe present disclosure, the brightness of the illumination light isvarying. Specifically, the second modulation cycle includes alow-brightness period and a high-brightness period. Illuminationbrightness in the low-brightness period is first-level brightness, andillumination brightness in the high-brightness period is second-levelbrightness. The first-level brightness and the second-level brightnessmay be constant values, or may be brightness ranges, in other words, theillumination brightness in the low-brightness period includes aplurality of brightness values, and the illumination brightness in thehigh-brightness period includes a plurality of brightness values. Whenthe first-level brightness and the second-level brightness are theconstant values, the constant value corresponding to the first-levelbrightness is less than the constant value corresponding to thesecond-level brightness. When the first-level brightness and thesecond-level brightness are the brightness ranges, any brightness of thefirst-level brightness is less than any brightness of the second-levelbrightness; or the light brightness of the light source when the lightsource is continuously driven at its rated current is the ratedbrightness, any brightness of the first-level brightness is less thanthe rated brightness, any brightness of the second-level brightness isnot less than the rated brightness, and a difference value between theaverage brightness of the first-level brightness and the second-levelbrightness (i.e., a value obtained by dividing a sum of the first-levelbrightness and the second-level brightness by 2) and the ratedbrightness is less than a specified threshold.

In each second modulation cycle, the spatial light modulator 150 isconfigured to modulate the illumination light based on a 2D imagecorresponding to each spatial angle, to obtain image light correspondingto each 2D image. In the present disclosure, an example in which thespatial light modulator 150 is a DMD is used for description. The DMD isprovided with a modulation area for receiving and modulating theillumination light, and the modulation area is provided with modulationunits arranged in pixels. Each modulation unit is specifically areflective micromirror, and each reflective micromirror may be in an“ON” state or “OFF” state. When the reflective micromirror is in the“ON” state, the reflective micromirror is used to reflect anillumination beam to the angle deflection apparatus 170, such that theillumination beam can be emitted from the projection lens and displayedon the projection screen. When the reflective micromirror is in the“OFF” state, the reflective micromirror is used to reflect anillumination beam to the outside of the angle deflection apparatus 170,such that the illumination beam does not enter the projection lens, andis not emitted from the projection display device 100. A light rayemitted by one reflective micromirror corresponds to one pixel in ato-be-displayed image.

The LSB is a minimum grayscale unit that can be realized by the spatiallight modulator. In the present disclosure, the LSB corresponds to atime length corresponding to a minimum brightness unit that can bemodulated by the spatial light modulator in an illumination timesequence. In the present disclosure, the second modulation cycleincludes a plurality of LSBs, and a sum of time lengths corresponding tothe plurality of LSBs constitutes the second modulation cycle. The timelength corresponding to the LSB corresponds to one reversal cycle of themodulation unit, which is denoted as a response time length t_(LSB), asshown in FIG. 2.

It should be noted that, during 3D video playback, a playback frame rateis preset or specified based on an actual demand, in other words, timecorresponding to the first modulation cycle is determined, and aquantity of 2D images obtained through parsing by the control apparatusbased on the stereo image data is determined based on an actuallyspecified algorithm. Therefore, when the first modulation cycle isdetermined, time corresponding to the second modulation cycle is alsodetermined. For example, if the frame rate is 60 Hz, modulation time ofone frame of stereo image, namely, the time length corresponding to thefirst modulation cycle, is: time corresponding to each color (namely,1)/60 Hz≈16.67 ms. If the control apparatus can split one frame ofstereo image into three 2D images based on the algorithm, the timelength corresponding to the second modulation cycle is 16.67/3≈5.56 ms.

In the present disclosure, the control apparatus 190 can obtain aspecified grayscale state set through modulation in the secondmodulation cycle by controlling the reversal cycle of the modulationunit of the spatial light modulator 150 in the determined secondmodulation cycle, namely t_(LSB), and controlling a brightness change ofthe illumination light emitted by the light source.

Assuming that it is necessary to display the 2D image split from thestereo image as an image with a bit depth of 5, if a traditional binaryPWM timing modulation method with constant illumination light is used todisplay the image with the bit depth of 5, 5 bit planes corresponding todifferent bit orders need to be obtained through division. A weightcorresponding to a bit plane of a lowest bit order is 2°, whichcorresponds to time corresponding to one LSB. Weights corresponding tobit planes of other bit orders are 2¹, 2², 2³, and 2⁴ respectively. Timecorresponding to a bit plane of a highest bit order is timecorresponding to 2⁴=16 LSBs. If image data of a pixel is binary 01111,the DMD is OFF in the time corresponding to the bit plane of the highestbit order, and is on in time corresponding to other bit planes. If imagedata of a pixel is 11010, the DMD is OFF in bit planes whose weights are2⁰ and 2² respectively, and is on in other bit planes. According to theabove rules, the DMD can obtain 32 grayscale states through modulationin time corresponding to the 5 bit planes, in other words, can displaythe image with the bit depth of 5. Minimum time required to realize animage with the bit depth of 5 by using the binary PWM timing modulationmethod with constant illumination light is time corresponding to 31LSBs. Therefore, when the bit depth of the 2D image is i, a time lengthrequired for modulating one frame of 2D image in a PWM modulation modeis: (2^(i)−1)*t_(LSB). However, the time length cannot meet the time ofthe second modulation cycle during 3D video display. That is, when aframe rate of a to-be-displayed 3D video is high, the traditional PWMtiming modulation method is unable to display a 2D image with a high bitdepth in a short time.

The present disclosure realizes image display with a higher bit depth ina shorter time by adjusting the time length corresponding to the LSB,the brightness of the illumination light in time corresponding to eachLSB and the ON or OFF state of modulation unit.

As shown in FIG. 3, to display the image with the bit depth of 5, timecorresponding to at least 5 LSBs is required, and corresponding time ofeach LSB corresponds to different brightness of the illumination light.A switch of a single lens in the time corresponding to the 5 LSBs iscontrolled to realize 32 illumination brightness values, namely, 32grayscale states, which are 0, L1, L2, L3, L4, L5, L1+L2, L1+L3, L1+L4,L1+L5, L1+L2+L3, L1+L2+L4, L1+L2+L5, L1+L3+L4, L1+L3+L5, L1+L4+L5,L1+L2+L3+L4, L1+L2+L3+L5, L1+L2+L4+L5, L1+L3+L4+L5, L1+L2+L3+L4+L5,L2+L3, L2+L4, L2+L5, L2+L3+L4, L2+L3+L5, L2+L4+L5, L2+L3+L4+L5, L3+L4,L3+L5, L3+L4+L5, L4+L5.

Certainly, during actual display, a quantity of LSBs included in thesecond cycle, namely, a time length corresponding to each LSB, may beadjusted based on an actual time length of the second modulation cycleand a bit depth of a to-be-displayed 2D image, and a time lengthcorresponding to one or more LSBs can be set to correspond to oneillumination brightness value. A time length corresponding to eachillumination brightness value may be the same or different.

In the present disclosure, in each second modulation cycle, namely, indisplay time of each frame of 2D image, the brightness of theillumination light is not constant, in other words, the brightness inthe low-brightness period and the brightness in the high-brightnessperiod in the second modulation cycle are different. Compared with thePWM modulation mode, the present disclosure is advantageous for eachmodulation unit to emit illumination light conforming to a light amountcorresponding to a pixel grayscale to the angle deflection apparatus 170in a relatively short time length, so as to help the projection displaydevice 100 to reduce the time length of the second modulation cycle.More second modulation cycles may be specified in the fixed firstmodulation cycle, that is, in display time of one frame of stereo image,the projection display device provided in the present disclosure isconducive to emitting image light corresponding to more frames of 2Dimages. After angle polarization, these frames of 2D images can besynthesized into one frame of stereo image, so as to display the stereoimage.

In an embodiment, in the second modulation cycle, the time lengthcorresponding to the LSB and the brightness of the illumination lightare adjusted to make the time length of the one or more LSBs correspondto one brightness value of the illuminating light, such that a 2D imagewith a specified bit depth can be obtained through modulation in thesecond modulation cycle, and it is also necessary to ensure that averagebrightness of the illumination light in the second modulation cycle isnot less than a specified threshold to ensure that an image obtainedthrough modulation meets a brightness requirement. For example, in thesecond modulation cycle, rated brightness of the varying illuminationlight is close to the rated brightness of the light source under therated current, or in the second modulation cycle, a ratio of the averagebrightness of the varying illumination light to the rated brightness is0.8 to 1.2.

In an implementation, the second modulation cycle includes thelow-brightness period and the high-brightness period. Average brightnessof the high-brightness period is greater than the rated brightness,average brightness of the low-brightness period is less than the ratedbrightness, and a ratio of overall average brightness of thehigh-brightness period and the low-brightness period to the ratedbrightness is 0.8 to 1.2.

In a specific embodiment, as shown in FIG. 4, the horizontal axis inFIG. 4 represents time, and a length of the horizontal axis in thefigure is one second modulation cycle, including (m+n) response timelengths t_(LSB), where m response time lengths correspond to mlowest-brightness sub-periods, namely, a first lowest-brightnesssub-period, a second lowest-brightness sub-period, . . . , and an m^(th)lowest-brightness sub-period, and n response time lengths correspond ton highest-brightness sub-periods, namely, a first highest-brightnesssub-period, a second highest-brightness sub-period, . . . , and ann^(th) lowest-brightness sub-period. The vertical axis in FIG. 4represents the brightness of the illumination light. In each secondmodulation cycle, the brightness of the illumination light is lowest inthe first lowest-brightness sub-period, highest in the n^(th)highest-brightness sub-period, and constant in each sub-period. Thebrightness of the illumination light increases stepwise from low to highin different sub-periods, or more specifically, brightness changes ofthe illumination light in different sub-periods are exponential. In thisimplementation, brightness of the illumination light in eachlowest-brightness sub-period meets the following formula:L_(1i)=L/2^(m+1−i), where 1≤i≤m, i is an integer, L_(1i), representsbrightness of the illumination light in an i^(th) lowest-brightnesssub-period, and L represents the rated brightness emitted by the lightsource at the rated current; and brightness of the illumination light ineach highest-brightness sub-period meets the following formula:L_(2j)=L*2^(j−1), where 1≤j≤n, j is an integer, L_(2j) representsbrightness of the illumination light in a j^(th) highest-brightnesssub-period, and L represents rated brightness emitted by the lightsource at the rated voltage.

As shown in FIG. 4, the brightness of the illumination light in thefirst lowest-brightness sub-period is L/2^(m), and brightness of theillumination light in a subsequent sub-period is twice brightness of aprevious sub-period. In other words, brightness values of theillumination light in the plurality of lowest-brightness sub-periods areL/2^(m), L/2^(m−1), L/2^(m−2), . . . , and L/2 respectively, andbrightness values of the illumination light in the plurality ofhighest-brightness sub-periods are L, L*2, . . . , and L*2^(n−1)respectively. L/2^(m) is lowest brightness that can be achieved for theillumination light in a pulse state. An amount of light emitted by onemodulation unit of the spatial light modulator 150 in the firstlowest-brightness sub-period (light brightness multiplied by a timelength of the first lowest-brightness sub-period) corresponds to agrayscale value that can be obtained by the spatial light modulator 150through modulation when the LSB is 1, which is also a difference betweenamounts of light corresponding to adjacent grayscale values. L*2^(n−1)is highest brightness that can be achieved by the light source 110 inthe pulse state. In the second modulation cycle, a total amount of lightemitted by each modulation unit corresponds to a grayscale value of themodulation unit. In this implementation, the brightness of theillumination light changes exponentially in two consecutive sub-periodsof each modulation cycle. In other implementations, the brightness ofthe illumination light decreases exponentially or changes according toanother numerical rule in each modulation cycle.

Average brightness of the illumination light in one modulation cycle isL_(mean)=(2^(n)−½^(m))*L/(m+n). A larger quantity of lowest-brightnesssub-periods leads to a larger decrease of the average brightness. If thebrightness of the illumination light in the second modulation cycle isrequired to be close to the rated brightness of the light source at therated current, or the ratio of the average brightness of the varyingillumination light in the second modulation cycle to the ratedbrightness is required to be 0.8 to 1.2, namely, L_(mean)≈L, the controlapparatus controls a quantity m of LSBs included in the low-brightnessperiod and a quantity n of LSBs included in the high-brightness period,such that the quantity m and the quantity n meet the followingrelationship: 2^(n)−n≈m+(½^(m)). When m=1, n=2; when m=2, n=2; when m=3;n=3; . . .

To achieve a bit depth of (m+n), time required to modulate one frame of2D image is about (2^(m+n)−1)*t_(LSB) in the traditional PWM modulationmethod, and is only (m+n)*t_(LSB) in the modulation method described inthe present disclosure. In other words, in the time for modulating oneframe of 2D image in the traditional PWM modulation method, about(2^(m+n)−1)/(m+n) frames can be obtained through modulation in thepresent disclosure.

Compared with traditional 2D display, the solution in the presentdisclosure can quickly realize grayscale adjustment in combination withbrightness adjustment of the illumination light, and has a high framerate, which is conducive to emitting projection images from a pluralityof angles, so as to realize 3D display.

In an implementation, m=5, n=3, and the second modulation cycle is 8response time lengths t_(LSB). Assuming that a minimum response timelength t_(LSB) is about 22 us, if the solution in this implementation isadopted, a minimum second modulation cycle is about 176 us, and about5682 frames can be displayed in 1 s. If a frame rate of multi-angle 3Ddisplay is set to 60 Hz, the projection display device 100 can obtain5682/6095 angles through division in each frame for projection display.

Multi-angle image data that is of a stereo image of each pixel and inputto the control apparatus 190 may include a plurality of pieces of 2Doriginal image data, and each piece of original image data correspondsto a projection angle. Since a plurality of angles corresponding toinput multi-angle image data may be inconsistent with a plurality ofprojection and emission angles of the projection display device 100, thecontrol apparatus 190 obtains corresponding stereo image data based onthe multi-angle original image data of each pixel, and splits each frameof stereo image data based on an algorithm to obtain a 2D imagecorresponding to each projection angle of the projection display device100. In each second modulation cycle, the spatial light modulator 150 isconfigured to modulate the illumination light based on the 2D imagecorresponding to each projection angle, to obtain image lightcorresponding to each projection angle.

The control apparatus 190 is further configured to send a deflectioncontrol signal, and the projection display device 100 further includesthe angle deflection apparatus 170. The angle deflection apparatus 170is configured to guide, to different spatial angles based on thedeflection control signal, a plurality of frames of 2D image lightemitted by the spatial light modulator 150 in the first modulationcycle, and the plurality of frames of 2D image light with differentspatial angles are projected onto the projection screen, to achieve a 3Ddisplay effect relative to human eyes. Brightness adjustment of theillumination light, control performed by a control unit, and adjustmentof a spatial angle of emergent light can be synchronously controlledbased on the deflection control signal and the light source controlsignal that are sent by the control apparatus 190 and a control signalof the on/OFF state of the modulation unit.

In an embodiment, a steady state of the modulation unit of the spatiallight modulator in the second modulation cycle is adjusted, such thatdifferent image frames have different spatial angles. As shown in FIG.5, I1, I2, and I3 are three different steady states of the modulationunit of the spatial light modulator. When the spatial light modulatorobtains different 2D images through modulation and emits the 2D images,the modulation unit is in a steady standby state. In each secondmodulation cycle, the modulation unit has a same steady-state angle, soas to ensure that a complete grayscale image is emitted. For example, ina 1^(st) second modulation cycle of the first modulation cycle, themodulation unit is in the I1 state to deflect a 2D image emitted in thecycle to a spatial angle corresponding to the I1 state; in a 2^(nd)second modulation cycle of the first modulation cycle, the modulationunit is in the I2 state to deflect a 2D image emitted in the cycle to aspatial angle corresponding to the I2 state; and in a 3^(rd) secondmodulation cycle of the first modulation cycle, the modulation unit isin the I3 state to deflect a 2D image emitted in the cycle to a spatialangle corresponding to the I3 state. It can be understood that a microelectro mechanical system can further be configured to deflect the imagelight to more than three projection directions in a time division mode.

In another embodiment, as shown in FIG. 6, the angle deflectionapparatus 170 includes a plurality of guide portions located on anoptical path of the image light based on a deflection signal timing, anddifferent guide portions are configured to guide the image light todifferent projection angles for transmission. As shown in FIG. 6, theangle deflection apparatus 170 is a guide array W. The guide array W isconfigured to deflect image light I with a same incident angle todifferent angles and obtain image light I1, I2 and I3 transmitted atdifferent angles. The guide array W includes at least a guide portionW1, a guide portion W2, and a guide portion W3. Each guide portion inthe guide array W vibrates repeatedly. In each second modulation cycle,one guide portion in the guide array W is located on the optical path ofthe image light emitted by the spatial light modulator 150, and is usedto refract the image light. Different guide portions are used to refractthe incident image light to different deflection angles, and obtain atleast image light I1, I2 and I3 transmitted at different deflectionangles. In another implementation, the guide array W reflects the imagelight I to a plurality of deflection angles in the time division mode.In an embodiment, the guide portion may be a designed polygonousscanning lens or the like.

The image light emitted by the angle deflection apparatus 170 at aplurality of different angles is projected onto the projection screen.The projection screen is configured to receive image light withdifferent deflection angles to display a stereo image. In animplementation, the projection screen is an angle-spreading screen toincrease an included angle between transmission directions of imagelight incident at different angles, such that the image light incidentat different angles can be separated more widely.

The present disclosure further provides a control method applied to theabove projection display device 100. A period in which the projectiondisplay device 100 displays one frame of stereo image is referred to asa first modulation cycle, one frame of stereo image is synthesized by aplurality of frames of 2D images transmitted in different directions,and a period in which the projection display device 100 displays oneframe of 2D image in one frame of stereo image is referred to as asecond modulation cycle. The control method provided in the presentdisclosure specifically includes the following steps.

S1: Control the light source to emit illumination light.

As shown in FIG. 1, in the present disclosure, the light source 110 isused to emit the illumination light. In each second modulation cycle,the light source 110 controls brightness of the illumination lightemitted by the light source 110 to change from first-level brightness tosecond-level brightness. The first-level brightness is less than thesecond-level brightness, and both the first-level brightness and thesecond-level brightness are brightness ranges. In the second modulationcycle, the brightness of the illumination light may be presented asbrightness values at a plurality of levels.

Each second modulation cycle includes a low-brightness period and ahigh-brightness period. The illumination light has the first-levelbrightness in the low-brightness period, and has the second-levelbrightness in the high-brightness period. Light brightness of the lightsource 110 when the light source 110 is continuously driven at its ratedcurrent is rated brightness. The brightness of the illumination light inthe low-rightness period is controlled to be less than the ratedbrightness, and the brightness in the high-brightness period iscontrolled not to be less than the rated brightness.

The light source 110 emits illumination light with different brightnessin at least two periods of the second modulation cycle, so as to helpshorten the second modulation cycle and improve a frame rate. Thebrightness of the illumination light in the low-brightness period isless than the rated brightness, and the brightness of the illuminationlight in the high-brightness period is not less than the ratedbrightness, so as to improve the frame rate and ensure brightness ofimage light emitted by the projection display device 100 while ensuringan image contrast.

S2: In the first modulation cycle, control, based on a plurality offrames of 2D images corresponding to one frame of stereo image, thespatial light modulator to modulate the illumination light to obtainimage light.

The control apparatus 190 obtains, based on multi-angle 2D originalimage data of each pixel, data corresponding to one frame of stereoimage, and splits the data corresponding to one frame of stereo image toobtain a 2D image corresponding to a spatial angle that can be obtainedby the angle deflection apparatus through deflection.

Stereo image data that is of one frame of stereo image of each pixel andinput to the control apparatus 190 may include a plurality of frames of2D original image data, and each frame of original image datacorresponds to a projection angle. Since a plurality of anglescorresponding to input multi-angle original image data may beinconsistent with a plurality of projection and emission angles of theprojection display device 100, the control apparatus 190 obtains thecorresponding stereo image data based on the multi-angle 2D originalimage data of each pixel, or splits received stereo image data based onan algorithm to obtain 2D original image data corresponding to eachprojection angle of the projection display device 100. The 2D image maycorrespond to a 2D image of a single base color, such as a red, green,or blue image. A plurality of images of different base colors aresynthesized into a color 2D image. In each second modulation cycle, thespatial light modulator 150 is configured to modulate the illuminationlight based on a 2D image corresponding to each projection angle, toobtain image light corresponding to each projection angle.

In an implementation, the low-brightness period includes mlowest-brightness sub-periods, the high-brightness period includes nhighest-brightness sub-periods, and m and n are positive integers. Indifferent sub-periods of each modulation cycle, the light brightness ofthe light source 110 is controlled to change exponentially.Specifically, the light brightness of the light source is controlled tobe L/2^(m+1−i) in an i^(th) low-brightness period, where 1≤i≤m, and i isan integer. The light brightness of the light source is controlled to beL*2^(j−1) in a j^(th) low-brightness period, where 1≤j≤n, and j is aninteger. Correspondingly, the spatial light modulator 150 is controlledto modulate the illumination light by using one data bit in a 2D imageof a corresponding pixel in each sub-period, and a time length of eachmodulation cycle is (m+n)*t_(LSB).

S3: In the first modulation cycle, control the angle deflectionapparatus to deflect image light corresponding to different frames of 2Dimages to different spatial angles.

The present disclosure provides two implementations of the angledeflection apparatus 170. It can be understood that another apparatusnot provided in the present disclosure can also be used to realize angledeflection.

S4: Use the screen to receive image light with different deflectionangles to display a stereo image.

It should be noted that, within the scope of the spirit or basicfeatures of the present disclosure, the specific solutions in theimplementations are mutually applicable, and various implementations inthe display apparatus 100 and the control method are mutuallyapplicable. For brevity and in order to avoid repetition, details arenot described herein again.

For a person skilled in the art, it is apparent that the presentdisclosure is not limited to the details of the foregoing exemplaryembodiments, and that the present disclosure can be implemented in otherspecific forms without departing from the spirit or basic features ofthe present disclosure. Therefore, the embodiments should be regarded asexemplary and non-limiting in every respect, and the scope of thepresent disclosure is defined by the appended claims rather than theabove description. Therefore, all changes falling within the meaning andscope of equivalent elements of the claims should be included in thepresent disclosure. Any reference numerals in the claims should not beconsidered as limiting the claims involved. In addition, it is apparentthat the word “including” does not exclude other units or steps, and asingular number does not exclude a plural number. A plurality ofapparatuses stated in the apparatus claims may also be implemented by asame apparatus or system through software or hardware. The words such as“first” and “second” are used to denote names and do not indicate anyparticular order.

Finally, it should be noted that the foregoing embodiments are onlyintended to describe, rather than to limit the technical solutions ofthe present disclosure.

What is claimed is:
 1. A projection display device, wherein a period inwhich one frame of stereo image is displayed is referred to as a firstmodulation cycle, and the projection display device comprises: a lightsource, configured to emit illumination light; a spatial lightmodulator, configured to modulate the illumination light based on aplurality of frames of 2D images corresponding to a stereo imageto-be-displayed, and sequentially emit, in the first modulation cycle,image light corresponding to the plurality of frames of 2D images; anangle deflection apparatus, disposed on an emergent optical path of theimage light, and configured to deflect the image light corresponding tothe plurality of frames of 2D images to different angles for emission;and a projection screen, configured to display the image light deflectedby the angle deflection apparatus.
 2. The projection display deviceaccording to claim 1, wherein the first modulation cycle comprises aplurality of second modulation cycles, and the spatial light modulatoremits image light of one frame of 2D image in the second modulationcycle; the projection display device further comprises a controlapparatus, which is configured to control the light source to emitillumination light with varying brightness in the second modulationcycle; and the control apparatus is further configured to control a timelength corresponding to a least significant bit (LSB) of the spatiallight modulator in the second modulation cycle and an ON status or OFFstatus of a modulation unit of the spatial light modulator in a timelength corresponding to each of the LSB, such that the spatial lightmodulator is capable of obtaining a specified illumination brightnessset through modulation in the second modulation cycle.
 3. The projectiondisplay device according to claim 2, wherein the second modulation cyclecomprises a low-brightness period and a high-brightness period, thelight source emits light with first-level brightness in thelow-brightness period and emits light with second-level brightness inthe high-brightness period, and the first-level brightness is less thanthe second-level brightness.
 4. The projection display device accordingto claim 3, wherein each of the first-level brightness and thesecond-level brightness is range brightness; and any brightness of thefirst-level brightness is less than any brightness of the second-levelbrightness; or average brightness of the first-level brightness is lessthan rated brightness of the second-level brightness; or lightbrightness of the light source when the light source is continuouslydriven at its rated current is rated brightness, any brightness of thefirst-level brightness is less than the rated brightness, any brightnessof the second-level brightness is not less than the rated brightness,and a difference value between the rated brightness and averagebrightness of the first-level brightness and the second-level brightnessis less than a specified threshold.
 5. The projection display deviceaccording to claim 3, wherein at least one of the first-level brightnessor the second-level brightness changes in a step-like manner, andbrightness in each step corresponds to a time length corresponding to atleast one LSB.
 6. The projection display device according to claim 5,wherein the low-brightness period comprises m LSBs, the high-brightnessperiod comprises n LSBs, m and n are positive integers, and brightnessof the illumination light in the low-brightness period satisfies thefollowing formula: L_(1i)=L/2^(m+1−i), wherein 1≤i≤m, where i is aninteger, and L_(1i) represents brightness of the illumination lightcorresponding to an i^(th) LSB; brightness of the illumination light inthe high-brightness period satisfies the following formula:L_(2j)=L*2^(j−1), wherein 1≤j≤n, where j is an integer, and L_(2j)represents brightness of the illumination light corresponding to aj^(th) LSB; and if the time length corresponding to the LSB is denotedas t_(LSB), then the second modulation cycle satisfies the followingformula: T=(m+n)*t_(LSB), where T represents the second modulationcycle.
 7. The projection display device according to claim 6, wherein2^(n)−n≈m+(½^(m)).
 8. The projection display device according to claim2, wherein the control apparatus is configured to generate a stereoimage from a plurality of frames of images of different image formationplanes, and then split the stereo image based on an algorithm to obtain2D images corresponding to different spatial angles; and the angledeflection apparatus is configured to deflect, to a correspondingspatial angle, image light corresponding to any 2D image and emitted bythe spatial light modulator.
 9. The projection display device accordingto claim 8, wherein the control apparatus controls, based on acorrespondence between the spatial angle and a steady state of themodulation unit, the modulation unit to perform deflection in differentsteady states when the spatial light modulator modulates differentframes of 2D images.
 10. The projection display device according toclaim 8, wherein the angle deflection apparatus comprises a plurality ofguide portions sequentially located on the optical path of the imagelight in the first modulation cycle, each of the plurality of guideportions is configured to deflect the image light of the 2D image to itsassociated spatial angle, and each of the plurality of guide portionsstays in the optical path for a period of time corresponding to thesecond modulation cycle.
 11. The projection display device according toclaim 1, wherein the projection screen is an angle-spreading screen. 12.The projection display device according to claim 4, wherein at least oneof the first-level brightness or the second-level brightness changes ina step-like manner, and brightness in each step corresponds to a timelength corresponding to at least one LSB.